When we choose rubber seals, the first consideration of the performance mainly includes its tensile strength, fixed-stretch stress, elongation, breaking elongation, breaking permanent deformation, and stress-strain curves. We collectively refer to the tensile strength. The tensile strength is the maximum tensile stress when the specimen is stretched to rupture. The fixed-stretch stress (the constant modulus) is the stress (modulus) reached at the specified elongation. Elongation is the deformation of specimen subjected to tensile stress, and the percentage of elongation increment with the ratio of the original length is expressed. Elongation at break is the elongation at the time of the specimen. The breaking permanent deformation is the residual deformation of the part of the specimen after tensile fracture.
Then, we consider the basic properties of rubber seals-hardness. The so-called hardness is the ability to resist the invasion of external pressure. The hardness of the rubber is partly related to some other performance. For example, the hardness of the rubber material, relatively high, the strength is larger, the elongation is small, the abrasion resistance is better, and low temperature performance is poor. High hardness rubber can resist crushing damage under high pressure. Therefore, the appropriate hardness should be chosen according to the working characteristics of the parts.
We know that rubber seals are often in a compressed state, then we need to consider the compression properties of rubber seals. Due to the viscoelastic rubber, compressive stress will decrease with time, and the compressive stress is relaxed, and the original shape is not restored after the pressure is removed, and it is characterized by compression and permanent deformation. These phenomena are more remarkable in high temperature and oil media. They can affect sealing performance of seals, and is one of the importance of adhesive material for sealing parts.
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